1. Field of the Invention
The invention relates to a tool for isothermal forging, consisting of two die halves, at least one of which is divided at least once.
2. DESCRIPTION OF THE PRIOR ART
Tools for isothermal forging are used for the comparatively slow plastic deformation of materials in the temperature region of superplasticity. The tool is here exposed to virtually the same high working temperature as the workpiece which is to be formed, and it is necessary in all cases to ensure that both the former and the latter are uniformly heated through. Inductive heating devices are customarily employed for heating the tool and in part also the workpiece as well as for keeping the working temperature constant. Hitherto, the tools were designed in such a way that the two die halves were each produced from one piece of a high-temperature alloy based on molybdenum or nickel. The frequently complicated shapes had to be worked out of the bulk of the tool blank, in most cases with the aid of electro-erosion. Installations of this type for isothermal forging have been disclosed in publications (for example D. J. Abson, F. J. Gurney, "Heated dies for forging and friction studies on a modified hydraulic forge press", Metals and Materials, December 1973; British Pat. No. 699 687; and U.S. Pat. No. 3,698,219).
One-piece tools, produced in the conventional manner, for isothermal forging are expensive since they require a high material consumption of high-temperature alloy which is sometimes difficult to work. Complicated shapes having deep grooves, small radii of curvature as well as sharp-edged and re-entrant corners cannot be produced by the customary machining methods and it is necessary to have recourse to very expensive processes, such as, for example, electro-erosion. Moreover, tools which have become useless as the result of local welding between the workpiece and the die, can only be repaired at high cost, and frequently cannot be repaired at all, because access to the affected point is impeded. In such cases, the total loss of a whole tool represents an essential further determining cost factor for the manufacture of complicated products.